Jonna S.B. Ahl

Methyl Farnesoate Levels in Male Spider Crabs Exhibiting Active Reproductive Behavior

The concentration of methyl farnesoate (MF) in the hemolymph and its synthesis by the mandibular organs (MOs) were investigated to determine whether this compound is related to the differences in the size of the reproductive system and the mating behavior among male morphotypes of the spider crab, Libinia emarginata. Large-claw abraded males displayed mating behavior under competitive conditions. They have the largest reproductive systems, their MOs synthesize large amounts of MF in vitro, and the concentration of MF in their hemolymph is high. Small-claw abraded males displayed mating behavior with receptive females only when isolated. These smaller crabs have intermediate-sized reproductive systems, their MOs synthesize the most MF, and they have the highest circulating level of MF relative to their body size. The unabraded males did not display mating behavior; their reproductive systems are smaller; their MO activity is low, as is their circulating level of MF. The strong relationship between MF levels and the intensity of reproductive behavior suggests that MF may be one of the driving forces behind mating behavior in Crustacea.

Methyl farnesoate appears to be a crustacean reproductive hormone

Summary Methyl farnesoate (MF) is an unepoxidated form of juvenile hormone III, which controls reproduction in insects and appears to serve the same function in Crustacea. MF is synthesized by the mandibular organs (MOs) and has been found in the hemolymph of both females and males in more than 25 species of crustaceans. MF is most actively synthesized by females during vitellogenesis. MF appears to be an active gonadotropin since implants of MOs into non-reproductives will increase gonad indices. In males, high titers of MF are associated with large reproductive systems and aggressive mating behavior.

Methyl farnesoate and the effect of eyestalk ablation on the morphogenesis of the juvenile female spider crab Libinia emarginata

Summary The effect of eyestalk ablation on morphogenesis and levels of methyl farnesoate (MF) in the hemolymph were investigated in juvenile females of the spider crab Libinia emarginata. The ablated crabs had significantly increased levels of MF in the hemolymph as early as 7 days post-ablation, which continued to increase during premolt. In the intact controls, MF levels in the hemolymph remained low throughout the intermolt and premolt periods. All ablated animals molted to giant juveniles, while the intact controls molted to the adult form. These results strongly suggest that there is a period of the molt cycle which is sensitive to elevated levels of MF in the hemolymph, and that MF has a juvenilizing effect on morphogenesis in L. emarginata and probably in other crustaceans as well.

MATING BEHAVIOR AND METHYL FARNESOATE LEVELS IN MALE MORPHOTYPES OF THE SPIDER CRAB, LIBINIA EMARGINATA (LEACH)

Abstract We presently recognize at least six male morphotypes in Libinia emarginata which differ with respect to their appearance and reproductive behavior. The primary reproductives have a large carapace, large claws and their exoskeletal epicuticle is worn away, giving them an “abraded” appearance. These animals also have large reproductive system indices (RI), and high methyl farnesoate (MF) blood levels. Smaller abraded males with short claws do not compete with the larger aggressive ones, but employ alternative tactics such as “sneak mating” and female mimicry. They also have large RIs and high levels of MF in their blood. Unabraded morphs of any size do not attempt to mate. Their MF levels are lower (usually one half that of the abraded males) as are their RIs, suggesting that they are in a state of reproductive diapause. Incompletely abraded males have intermediate levels of MF and will attempt mating in the absence of the large-claw abraded ones. This relationship between behavior and hormone level suggests that MF may be involved in determining the type of mating behavior displayed by the different male morphotypes.

The pubertal molt in Crustacea revisited

Summary It is generally accepted dogma that sexual maturation in decapod crustaceans takes place after the “molt of puberty” to the adult form. However, in many instances, sexual maturation may take place before the “pubertal molt” resulting in the presence of polymorphic males with various mating strategies within a population. Male polymorphism is common in the spider crab Libinia emarginata, and the morphotypes differ with respect to body length and relative claw size. However, all reproductive individuals are recognized by the absence of the velvety epicuticle which covers the exoskeleton of recently molted individuals. The loss of the epicuticle is gradual, and during this time the reproductive system increases in size, methyl farnesoate increases in the hemolymph, and mating behavior is initiated. Male polymorphism, therefore, is evidence that the terminology “molt of puberty” is inappropriate and should be replaced with “differentiational” or “morphometric” molt.

Exoskeletal Abrasion as an Indicator of Reproductive Readiness in the Spider Crab Libinia Emarginata

ABSTRACT Patterns of exoskeletal abrasion on the carapace of long-clawed males of the spider crab Libinia emarginata appeared to follow specific sequences throughout the year. The degree of abrasion coincided with the enlargement of the reproductive system and increased levels of methyl farnesoate in the hemolymph. The patterns of abrasion apparently marked the time elapsed since the last molt, and when the abrasion extended beyond the midcarapace, it appeared to indicate increased reproductive readiness.

Ecdysteroids and juvenoids in two male morphotypes of Libinia emarginata

Two forms of the large-clawed male spider crab, Labinia emarginata, from the same molt stage, were examined to determine possible roles of ecdysteroids and juvenoids (methyl farnesoate) during maturation of the reproductive system and mating behavior. These forms are distinguished by the condition of the epicuticle covering the exoskeleton, abraded (worn away) and unabraded (intact), and mating behavior, active and inactive, respectively. Methyl farnesoate (MF) levels in the blood are high during active reproduction (abraded males)—mating, mate guarding and male competition; but, when the animals are in reproductive diapause (unabraded males), these levels are low. Ecdysteroids are found primarily in the testes of both male types. However, the amounts detected are highest in the non-reproductive unabraded males, and lowest in the actively mating abraded ones. It appears that ecdysteroids may function early in maturation in unabraded animals by making the gonad competent, while MF may be functioning in mature males with developed reproductive systems and exhibiting mating behavior.

Seasonal differences in methyl farnesoate esterase activity in tissues of the spider crab Libinia emarginata

Summary Methyl farnesoate (MF), an unepoxidated form of insect JH III, is present in Crustacea. MF is synthesized by the mandibular organs and is degraded to fomesoic acid (FA) by peripheral tissues. In this study we investigated MF degradation by esterases in hepatopancreas, ovary, testes and hemolymph of the spider crab Libinia emarginata collected at different times of the year to determine seasonal differences. The conversion of MF to FA varied among the tissues. In the summer, the hepatopancreas showed the greatest esterase activity (52.8% conversion in females and 59.16% in males), and it was twice as high (28.86%) in ovaries than in the testes (12.16%), but was low in the hemolymph of both sexes (10.84% in males, and 6.97% in females). In the fall, the conversion of MF to FA was significantly reduced in all tissues (ovary 8.55%, testes 6.21%, hepatopancreas 10.22%, hemolymph 3.96%). Eyestalk ablation of animals in the fall restored MF esterase activity to summer levels. When tissues from these anim...

METHYL FARNESOATE BINDING PROTEINS IN TISSUES OF THE SPIDER CRAB, LIBINIA EMARGINATA

Methyl farnesoate (MF) binding proteins (MFBPs) were found in the ovaries, testes, accessory glands, and hemolymph of the spider crab Libinia emarginata, by photoaffinity labeling the tissues in vitro with tritiated farnesyl diazomethyl ketone ([3H]-FDK). Specificity was demonstrated by competitive displacement of [3H]-FDK with MF. SDS-PAGE followed by fluorography revealed several labeled proteins in the hemolymph and testes with molecular masses ranging from 29 to 116 kDa, and two in the ovary that were 97 and 70 kDa. Tissues from reproductive animals bound twice as much label per gram weight compared to those that were from non-reproductive crabs.